Indoor Air Quality related problems, often referred to as “SICK BUILDING SYNDROMES” costs North America well over 100 Billion dollars each year in health care, absenteeism, lost production time and lost revenue.
Buildup of biological contaminants such as bacteria and molds onto the air conditioning coils has been identified as a major cause of the sick building syndrome. Those living organisms eventually release their toxins in the indoor air. Even in very small quantities, these toxins are extremely potent and can trigger violent responses from the human immune system. Such symptoms are commonly called allergies. The microorganisms found in buildings or workplace are viruses, bacteria, and their components, such as endotoxins, fungi and their metabolic products such as mycotoxins and antigens.
Most environments contain a large variety of bacteria. Health risks increase only when the pathogens bacteria concentration is amplified in an indoor environment and these organisms or their by-products are suspended and successfully airborne towards the breathing zone. Legionnaire's disease, some pneumonias, and tuberculosis are airborne infectious diseases caused by bacteria (see table 1). Bacteria can also cause humidifier fever and hypersensitivity pneumonitis.
Endotoxins are components of a bacterial cell. More precisely, they are components of the outer membrane of some bacteria. Dangerous levels of airborne endotoxins have been reported in numerous work environments, including offices and laboratories. They can cause fever and malaise, changes in white blood cell counts, and respiratory and gastrointestinal problems (see table 1).
Fungi exist in over 100 000 known species. Microscopic fungi include yeasts and molds. Most fungi produce spores (structures whose role is propagation) that are carried by the air. The diameter of these spores varies from approximately 1 to 60 microns. Most substances containing carbon, abundant in indoor and outdoor environments, can serve as nutrients for molds. Accumulation of humidity in the indoor environment is the most important factor to be controlled to limit fungal growth.
Some fungi can invade living cells and cause infectious diseases. However, several molds produce proteins or glycoproteins that are highly antigenic i.e. capable of producing an immune response and can cause, as reactions, hypersensitivity diseases or allergies in susceptible individuals. These allergy reactions include rhinitis, allergic asthma and extrinsic allergic alveolitis. Growing molds may also produce several volatile organic compounds. These volatile compounds cause the characteristic moldy odour, among other things.
Antigens are organic substances capable of producing an immune response in humans. Practically all living organisms contain proteins; glycoproteins or polysaccharides with antigenic potential. This is a reason why several microorganisms (bacteria, fungi, protozoa, acarids, etc.) have an impact on health via the action of antigens on the immune system.
Of all the hyper sensibility diseases, only hypersensitivity pneumonitis, allergic asthma, allergic rhinitis and allergic aspergillosis are known as being a result of exposure to airborne antigens. The cause effect relationship for microbial allergens is well known, but the complete characterization of the dose-response relationship is not.
Water reservoirs and air conditioning units cooling coils where warm water condenses are good growth media for some bacteria, fungi or protozoa. Consequently, ventilation system components, particularly some types of humidifiers, can aerosolize droplets from water reservoirs and therefore are of special interest due to the production of small antigenic hypersensitivity pneumonitis have occurred in individuals when building humidification systems were contaminated.
In buildings, the most important sources of antigens relating to human health are mites, cockroaches, and molds. All these organisms produce antigens, which can cause allergic asthma and allergic rhinitis. Dust mites (acarids) and their droppings that have accumulated in bedding, furniture or in places where the relative humidity and temperature are favourable, also produce antigens.
TABLE 1Biological air contaminantsBiologicalcontaminantsHealth EffectsMajor Indoor SourcesBacteriaPneumonia, Fever,Water reservoirs, hot water or hotHypersensitivity,surfaces, humidifier, cooling coilsAsthma, PneumonitisFungiAsthma, Rhinitis,Outdoor air, spores, birds, plants,infections, cancerdamp surfaces, cooling coilsProtozoaInfectionWater reservoir, humidifierVirusesInfectionWater reservoir, humidifierAlgaeAsthma, RhinitisOutdoor AirGreen PlantsAsthma, RhinitisOutdoor air, pollenArthropodsAsthma, RhinitisCarpets, feces, mattresses, dustMammalsAsthma, RhinitisDogs, cats, skin scales, salivaThe Indoor Air Quality Problem
It is now common knowledge that the energy efficient designs of the 1970's resulted in tighter building envelopes with improved insulation and low energy consuming ventilation, without operable windows, and that under these conditions, indoor pollutants were not sufficiently diluted with fresh air. Furthermore, an increase in indoor pollutant sources have been noted. New building materials, products, and furnishing emit a significant number of potentially hazardous chemicals into the air. The resulting situation is an increase in contaminants circulating through the indoor environment, with insufficient outside air introduced to dilute the contaminants.
Indoor air quality (IAQ), is a complex issue, much more so than any single environmental issue. There are hundreds of pollutants that affect IAQ and thousands of sources. Research indicates that more than 900 different contaminants are present in indoor environments.
If needs for comfort, health, and well-being are not satisfied, building users may begin to complain of symptoms which are associated with poor IAQ. Headaches, burning and itching eyes, respiratory difficulties, skin irritation, nausea, congestion, cough, sneezing, and fatigue are some of the common complaints. One of the most common IAQ complaints is that “there's a funny smell in here”. Odors are often associated with a perception of poor air quality.
An increasing percentage of the population is becoming more sensitive to a number of chemicals in indoor air, each of which may occur at very low concentrations. The existence of this condition has been identified as Multiple Chemical Sensitivity (MCS) and is currently the object of medical research.
According to EPA, the effects of Indoor IAQ problems are often non-specific symptoms rather than clearly defined illnesses. Although they can be vague, the symptoms seem generally worse after a day in the workplace and may altogether disappear when the occupant leaves the building.
Legionnaire's disease, tuberculosis and hypersensitivity pneumonitis are examples of building related illness that can have serious, even life-threatening consequences.
In light of this, it is easily understandable why indoor air needs to be efficiently purified from biological contaminants.
U.S. Pat. No. 5,817,276 entitled “Method of UV distribution in an air handling system” issued on Oct. 6, 1998 and naming Forrest B. Fencl at al., as inventors, describes a system where UV lamps are positioned in a HVAC system downstream of the heat exchanger coil, thus facing the air flow.
Fencl's method has at least four major drawbacks.
Direct air flow on the UV lamp cools it down by convection. A cooler lamp will display a lower UV output. Measurements by lamp manufacturers have shown that the germicidal UV emission drops by as much as 50% when direct air velocity over the lamp goes from 100 ft/min to 700 ft/min. To obtain the same UV irradiation, one must use twice the number of lamps or use expensive and short-life hot lamps with plasma arc temperature booster. Facing the flow, the lamps can collect some oily aerosols and dirt that will further inhibit their UV emission overtime.
By placing the UV lamps facing the outlet of the cooling coil, the inlet face where most of the water condensation and where most of the dust and other bacteria nutrients are normally accumulated is not directly irradiated. Its irradiation relies on the UV reflectivity of the coil material. It is at best 60% when the coil is made of clean aluminum. As the coil gets dirty, this UV reflection coefficient drops very quickly. Fencl is relying on the coil material UV reflection properties to achieve good results. This is a parameter that Fencl cannot control and that can dramatically impair the effectiveness of the invention.
Fencl states that the lamps must be placed over the coil surface in such a way as to provide a uniform irradiation distribution across the coil. Since the condensed water runs down the coil by gravity, the molds and bacteria concentration is most likely to occur at the bottom of the coil. In that view, a uniform irradiation pattern is certainly not the most efficient for the circumstances.
The use of a flat surface (see Fencl's FIG. 4) as a back reflector for the UV lamp allows for the loss of a large portion of the UV radiation. Even if the lamp is mounted very close to the coil, which is not very well suited for a “uniform irradiation”, a portion of the radiation that lies behind the 180 degree sector facing the coil cannot be reflected and will be lost.
By placing lamps on the plane perpendicular to the coil to provide uniform irradiation, the bottom area and coil corners where the water runs will not be sufficiently irradiated by the ultraviolet lamps and bacteria and mold will grow in these areas.
Furthermore, by irradiating the coil with an “open” lamp, the UV rays are allowed to irradiate and ultimately destroy any plastic or rubber parts in the air handler that the UV rays contact. Examples of such parts include wires, controls, flexible ducts and plastic drain pans.